Re: Stable GnuPG interface, git should use GPGME

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

On Fri, Mar 10, 2017 at 11:00 AM, Bernhard E. Reiter
<bernhard.reiter@intevation.de> wrote:
> Dear Git-Devs,

I haven't contributed to Git's GPG code, but I'm taking the liberty of
CC-ing some people who have.

> git uses an pipe-and-exec approach to running a GnuPG binary
> as writen in the documentation [1]:
>
>     gpg.program
>            Use this custom program instead of "gpg" found on $PATH when making
>            or verifying a PGP signature. The program must support the same
>            command-line interface as GPG
>
> please consider using libgpgme interfacing to GnuPG, because the gpg
> command-line interface is not considered an official API to GnuPG by the
> GnuPG-devs and thus potentially unstable.
>
> == Details
>
> I'm involved in GnuPG development. For most applications using libgpgme is the
> way what GnuPG-devs would recommend, also see
>
>   https://wiki.gnupg.org/APIs .
>
> GnuPG devs are making a good effort of trying to keep the command-line
> interface stable, though it is not for sure. Git is only using a small part
> of the interface, so the risk when keeping the current way is small.
> Still I believe git's stability and usability would profit when moving to
> libgpgme, especially with the coming move to GnuPG 2.2, better diagnosing
> messages and for cross-plattform usage.
>
> == Usability problem with `gpg2` vs `gpg`
>
> My use case today was signing and git by default found the `gpg` binary by
> default and the command failed. The reason is that I have `gpg2` installed
> and most applications use it right away. So git failed signing because
> the .gnupg configuration of the user was not ready for the old `gpg` which is
> still installed on Debian GNU/Linux for purposes of the operating system. If
> git would have used libgpgme, gpgme would have choosen the most uptodate
> version of `gpg` available (or configured) without me intervening via
> gpg.program. Now because of this problem you could adding a check for `gpg2`
> and fallback to `gpg`, but even better would be to move to libgpgme. >:)

I'm on Debian but haven't had these issues. What's your gpg & gpg2
--version & Debian release? And what in particular failed?

And what git version was this? I see we've had a couple of workarounds
for gpg2, in particular Linus's v2.8.4-1-gb624a3e67f, but if you have
v2.10.0 or later that won't fix whatever issue you had.

Using the library sounds good, but a shorter-term immediate fix would
be to figure out what bug you encountered in our use of the
command-line version, and see if we've fixed that already or not.
Regardless of what we do with a gpg library in the future some distros
might want to backport such a small patch if we can come up with it.

> Best Regards and thanks for maintaining Git as Free Software,
> Bernhard
>
> == how to respond
>
> ps: Please copy me on replies as I am not on git@vger.kernel.org.
> pps: I've copied gnupg-devel@ so they can see I've send this report, you don't
> have to.
>
>
> [1]
> https://github.com/git/git/blob/3bc53220cb2dcf709f7a027a3f526befd021d858/Documentation/config.txt
> search for 'gpg.program'.
>
> --
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